Major advances have been made in our understanding of the regulation of the molecular machinery of apoptosis in vitro. Molecules linking proliferation and apoptosis in healthy cells are being identified and here apoptotic cell death provides the 'fail-safe' mechanism to counteract excess proliferation. More recently, pioneering work on the regulation of apoptosis, in animal models of tumour development, has shown that suppression of apoptosis in the presence of a proliferative stimulus is sufficient for tumour development. Progress has also been made towards clarifying the contribution of drug-induced apoptosis to tumour response. With increasing evidence that failure to engage apoptosis after drug treatment contributes to drug resistance in vivo comes renewed confidence that new therapeutic approaches based on drug targets in apoptotic pathways will improve the treatment of cancer patients. As ever, tumour specificity is the major issue to be resolved.